1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method, and more particularly to an image forming apparatus and an image forming method which are suitable for detecting a phenomon that a recording sheet adheres to a roller member such as a pressurizing roller and a fixing roller forming a thermal fixing device or to a fixing film, to be wound around the latter.
2. Description of the Related Art
There is widely used an image forming apparatus which transfers a toner image formed on a photosensitive drum onto a recording sheet, and thermally fixes the toner image on the recording sheet by a thermal fixing device having roller members such as a fixing roller and a pressurizing roller to form an image on the recording sheet. In the image forming apparatus using the thermal fixing device of this type, however, if winding of a recording sheet to a roller member such as the fixing roller and the pressurizing roller cannot be detected and the image forming apparatus is operated with tip of the recording sheet wound around any of the roller members, the recording sheet is fully wound around the roller member, which makes it difficult to carry out a jam removing operation.
Therefore, an image forming apparatus and an image forming method are demanded, which positively prevent a recording sheet from being wound around a roller member.
It is an object of the present invention to provide an image forming apparatus and an image forming method which are capable of positively preventing a recording sheet from being wound around a conveying means that conveys the recording sheet.
To attain the above object, in a first aspect of the present invention, there is provided an image forming apparatus that forms an image on a recording sheet, comprising conveying means for conveying the recording sheet while rotating, the conveying means having a recording sheet passing area, voltage applying means for applying voltage to the conveying means, voltage detecting means for detecting voltage related to the conveying means in the recording passing area, temperature detecting means for detecting a temperature of the conveying means, threshold voltage setting means for setting a threshold voltage corresponding to the temperature detected by the temperature detecting means, and recording sheet winding detecting means for detecting whether the recording sheet is wound around the conveying means, based upon the threshold voltage set by the threshold voltage setting means and the voltage detected by the voltage detecting means.
Preferably, the recording sheet winding detecting means determines that the recording sheet is wound around the conveying means, when the voltage detected by the voltage detecting means is not higher than the threshold voltage threshold voltage set by the threshold voltage setting means.
More preferably, the threshold voltage setting means sets the threshold voltage to a value variable with the temperature detected by the temperature detecting means.
For example, the threshold voltage setting means sets the threshold voltage to a first threshold value when the temperature detected by the voltage detecting means is not lower than a predetermined value at which the threshold voltage is to be switched, and sets the threshold voltage to a second threshold value when the temperature detected by the voltage detecting means is lower than the predetermined value.
The second threshold value is higher than the first threshold value.
Preferably, the image forming apparatus comprises control means for controlling the conveying means, and the control means controls the conveying means such that the recording sheet is inhibited from being conveyed when the recording sheet winding detecting means detects that the recording sheet is wound around the conveying means.
In a preferred embodiment, the conveying means has a pair of rollers that convey the recording sheet interposed therebetween, and wherein the recording sheet winding detecting means detects whether the recording sheet is wound around at least one of the rollers.
Preferably, the pair of rollers comprise a pressurizing roller that applies pressure to the recording sheet, and a fixing roller that carries out a thermally fixing operation on the recording sheet, the voltage applying means applying voltage to the pressurizing roller, the temperature detecting means detecting a surface temperature of the pressurizing roller, and the recording sheet winding detecting means detecting whether the recording sheet is wound around the pressurizing roller.
Preferably, the recording sheet winding detecting means is responsive to turning-on of power supply of the image forming apparatus, for detecting whether the recording sheet is wound around the conveying means.
To attain the above object, in a second aspect of the present invention, there is provided an image forming method of forming an image on a recording sheet, comprising a threshold voltage setting step of detecting a temperature of conveying means for conveying the recording sheet while rotating, and setting a threshold voltage corresponding to the detected temperature, a voltage detecting step of detecting voltage related to the conveying means, and a recording sheet winding detecting step of detecting whether the recording sheet is wound around the conveying means, based upon the threshold voltage set in the threshold voltage setting step and the voltage detected in the voltage detecting step.
Preferably, in the recording sheet winding detecting step it is determined that the recording sheet is wound around the conveying means, when the voltage detected in the voltage detecting step is not higher than the threshold voltage threshold voltage set in the threshold voltage setting step.
More preferably, in the threshold voltage setting step the threshold voltage is set to a value variable with the detected temperature of the conveying means.
For example, in the threshold voltage setting step the threshold voltage is set to a first threshold value when the the detected temperature of the conveying means is not lower than a predetermined value at which the threshold voltage is to be switched, and the threshold voltage is set to a second threshold value when the the detected temperature of the conveying means is lower than the predetermined value.
The second threshold value is higher than the first threshold value.
Preferably, the image forming method comprises a control step of controlling the conveying means such that the recording sheet is inhibited from being conveyed when in the recording sheet winding detecting step it is detected that the recording sheet is wound around the conveying means.
Also preferably, the image forming method comprises a control step of controlling the conveying means such that the recording sheet is allowed to be conveyed when in the recording sheet winding detecting step it is not detected that the recording sheet is wound around the conveying means.
In a preferred embodiment, the conveying means has a pair of rollers that convey the recording sheet interposed therebetween, the pair of rollers comprising a pressurizing roller that applies pressure to the recording sheet, and a fixing roller that carries out a thermally fixing operation on the recording sheet, and wherein the threshold voltage setting step comprises detecting a temperature of the pressurizing roller, and setting the threshold voltage corresponding to the detected temperature, the voltage detecting step comprises detecting voltage applied to the pressurizing roller, and the recording sheet winding detecting step comprises detecting whether the recording sheet is wound around the pressurizing roller.
Preferably, the recording sheet winding detecting step is executed when power supply of an image forming apparatus that executes the image forming method.
The above and other objects, features and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.